1. Field of the Invention
The present invention generally relates to complementary metal oxide semiconductor (CMOS) and other complementary transistor structures, and more particularly to an improved structure that includes differently sized spacers for the different types of transistors to provide improved spacing of the source and drain extensions.
2. Description of the Related Art
As CMOS devices shrink, the source and drain extensions and junctions are required to be shallower to prevent the undesirable short channel effect. As the consequence of the shallower extensions and junctions, the resistance of the source and drain extensions increases sharply, resulting in lower drive and poorer performance. The current processes form a spacer of the same size for PFET and NFET before junction implants. Because PFET junction/extension dopants, such as boron, diffuse faster than the NFET junction dopant (i.e., As), spacer size is normally determined by the PFET requirement. However, this prevents the NFET's performance from being fully realized. Additionally, the long PFET extension results in a high series resistance. The invention described below addresses these issues.